Electric motor servo control system



Sept."28, 1948. J. F. EMERSON ELECTRIC MOTOR SERVO CONTROL SYSTEM FiledDec. :51, 194:

--,-- TO CRAFT cconaon. SURFACE- INVENTOR. fill IL I. Emerson.

ATTORNEY 3 Leads 3 and I are further tapped at points II and 2! toprimary winding ll of a power transiormer 3|, the secondary coil 32 ofwhich is connected to stator coils 33, I4 and ll of said inductivedevices 28, I and 21 on one side by lead I and through lead andresistors II, 31 and II in series with the other side oi the statorcoils a, 84 and 38. Inductively coupled with the respective stator coilsare rotors II, it and ll; which in their turn are connected in series tothe two-stage resistance coupled amplifier network A from potentiometersl2, l3 and 44 con necting with control grid ll of said amplifier networkThe inductive devices 2!, II and 21 are such that the voltage inducedinto rotors II, I. and H will vary'with the position of each rotor withrespect to its stator.

The signal voltage at grid ll will be the vectoral sum of the voltagesintroduced by, potentiometers' 42, 43 and ll. For proper operation,these voltages must be in phase, either zero degrees or 180 degrees inorder that they will add algebraically. This is provided by adjustingresistors 38, 31 and ll, together with 'the proper total or seriesresistance of potentiometersfl, l3 and 44. For example, increasing theresistance of potentiometer 42, produces phase 'shiit in the oppositedirection i'rom increase in resistor 3!. Thedesired ratio of signals isobtained by adjusting the taps II, II and It 01 'potentiometers 42, 48and 44.

The resistance'coupl'ed amplifier comprises a pair or electron tubes l1and 48 connected in cascade which are responsive to the algebraic sum ofthe resultant signal voltages introduced by the inductive devices 2|, 2|and 21 and pro- 7 vportionally mixed by said potentiometer-s12, 48 i and44, to thereby provide the amplification required'bei'ore applying thesignal to tubes "II and II of a discriminator unit, hereinafterdescribed. The amplifier electron tubes l] and ll are associated in theusual amplifier network with resistors ll, II, I, 2 and I8 and con-'sideiby leads I and "to grids 38 and 8! ara 4 former 3i, throughwindings II and II, respectively. paralleled with input filtercondensers N and 81. Since windings a and 24 are connected to oppositeends of winding .23 the voltages are of opposite polarity, that isphased 180 degrees with respect to each other.

The internal current oi tubes II and H does not fiow through the biasresistors II and II, so these resistors canbe high in value and requirelow current. For these'reasons a simple resistance-capacity filter issatisfactory for filtering the output of the network oi rectifier It..The cathodes 12 and "A are thus made positive with respect to theirrespective grids Cl and II. ior fir! si n by voltage divider resistorsII and This bias voltage of tubes II and Hissufiicienttopermitonlysmallamountsotplatccurrangedinparallelpathstoeachotheringrid'controlled halt wave rectifier tubes I! and II through condenser II, andare so arranged that the voltage from the amplifier has approximately-sero degrees or 180 degrees phase relation with respect to one or theother of the cathode to plate voltages of the tubes. 10 and H.

The arrangement of the circuit oi tubes II and II and selection of theproper' type tube has made it possible to reduce the'weight, she andpower'consumption oithe system. 'l'brtheselectionoitubesllandllislargelydex'thevoltagetoplatellottubellwilltermined by the plate current that will fiow for f zero gridto cathodevolts at peak plate voltage. each tube II and II providing half waverectifie cation,soastointroducedirecteurrentintransformer windings 23and II. Condensers l4 and llareinputfiltercondenserssuchasusually usedwith half wave rectifiers having inductive loads which are supplied bysaturating transformer coils :3 and 2|.

Tubes II and H receive plate voltage as herei inbeiore mentioned, atpower supply irequency irom center tapped ttB oi power transnegativehaii' cycle, thereby preventing the rent to iiow during the maximumpositive values of plate voltage, the average currents, forclample,beingiimitedtoabout.002 ampere-for zero.-

signal. This is desirable, since the saturable transformers II andwillthen drawtheminimum magnetizing current consistent with goodsensitivity for small signals.

Operation Refen'ingfotheopmflm. whenno variation.

is produced in the several variable inductive coupling devices II, Itand 21, the signals at both grid Ilandlloitubes'llandll areseroso thattransformers ll and II are balanced and the current output through leadsI and I from primaries "-l! and llll is zero because the the secondaries|'I--ll and ll-It are in series age signal applied to control adds itand II of tubes" and ILtheindexvoitageoi plate" and associatedscreengridIla oitube ll-mightalso begoingthmfllhapositivehali cycle andplatellandassociatedscreengridllaoitube'llwmild beingthroughapositivehaiicyclebutthecon gr ds'landllwillthenbegdngthroughoicurrent intube'll,becausetheplateandsereerigridvoltageoithlstubearephas'edatlwdegreel irom-thoseoitube'll.

The foregoing operation, results in In unbalance between transiormers 2.and II, ducingadirectcurrentinsaturatingwmdingfl,thatisnotbalancedbyanequalcurrentinwindingjl.Asa.resultoisirchcurrentfiow.flsscore oi transformer 2' decrease;inpermeability so that voltage induced in secondary winding lI-IIwillbedecreasedinvalmcaasingantmbalanceinthenetworkoithetransiormerstlandll,

. resulting in acurrent fiow at output'leadsj and Iofonephasetowindingflotthetwo-phne motor. Theamountoi unbalanee depend upon the signalamplitude until .maximum saturating current flows or the core iscompletely saturated.

The reverse of this operation occur upon angular movement of thevariable inductive coupling devices 25, 28 and 21 in the oppositedirection thereby reversing the phase of the signal, whereupon the tube70 will conduct no current and tube 1i will conduct current in the samemanner as described above in connection with tube 10.

It obviously follows that the direction of motor torque is reversed whenthe phase of the amplifier applied voltage is reversed since secondary"-48 i in opposition to secondary ll-il. This is accomplished byreversing the phase of the signal voltage from variable inductivecoupling devices 25, 28 and 21 thus causing greater direct current inwinding 24 compared to winding 22 to unbalance transformers 20 and 2i.

A condenser I0 parallel with winding 22 of motor I may be used for powerfactor correction and should tune winding 22 for unity power factor atthe operating frequency.

Rotor ll of motor H when rotated in either direction by a signal voltageintroduced in winding 22 is connected through a transmission system,such as represented broadly by gears 22 and I2 and a shaft 84 to one ofany objects being controlled, such as a rudder or the like, not shown,and a shaft 85, which is suitably connected to the rotor ll of thevariable-inductive coupling device 21. v

Shaft 24 angularly positions an object or control in accordance with thedirection of motor torque and shaft 85 is arranged to return the rotorll of the inductive device 21 to null position in synchronism with thenew position of the controlled object and in synchronism with the motorrotor 8|, which deenergizes after having driven said object or controlto its new position.

There is thus provided a novel electrical servo system for automaticcontrol of mobile objects, such a; marine craft, aircraft and the lik'e,which is materially compact and reduced in weight by the elimination ofsubstantially all heavy and bulky apparatus heretofore consideredessential to produce sufficient power to operate the craft controls.

Also, the present novel electrical system has been provided so that aplurality of signal variable inductive coupling devices actuated bycondition responsive indicators of the axial position and course of acraft are arranged. so that the algebraic sum of the controlling signalsare automatically proportioned in a single circuit arrangement and thenamplified through a simplified tube circuit for either positive ornegative operation of the controls of the craft on which the system hasbeen installed.

Although the present invention is only described and illustrated indetail for one embodiment thereof, it is to be expressly understood thatthe same is not limited thereto. Various changes may be made in designand arrangement of the embodiment illustrated, as will now be apparentto those skilled in the art.v For a definition of the limits of theinvention. reference should be had to the appended claims.

What is claimed is:

1. The combination with at least two variable inductive devices adaptedfor developing separate signals of changing phase and amplitude and areversible motor energized in accordance with ;he algebraic sum of saidsignals together with a members connected with each other in series aidving relation, A. C. output windings on the outer legs of both of saidcore members and connected in series opposed relation whereby normallythe system is balanced and no current is induced to flow in said outputwindings in response to A. 0. current flow in said supply windings, asaturating winding on the central leg of each of said core memberswhereby in response to current flow in one or the other of saidsaturating windings the system is unbalanced to provide an A. C. currentat said output windings, means connecting said saturating windings tosaid electronic members, and means connecting said out put windings tosaid motor.

2. The combination with at least two variable inductive devices adaptedfor developing separate signals of changing phase and amplitude anda twophase induction motor energized in accordance with the algebraic sumofsaid signals together with a controlled member driven by said motor,of amplifying means connected to said devices and responsive to saidsignals as well as to the phase thereof for determiningthe energizationand the direction of rotation of said motor. said means comprising apair of electronic members, one or the other of which becomes conductivedepending upon the phase of said signals, a pair of magneticallypermeable core members, each core member :being formed with a centralleg and a pair of spaced parallel outer legs, A. C. supply windings onthe outer legs of both of said core members connected with each other inseries aiding relation. A. 0. output windings on the outer legs of bothof said core members and connected in series opposed relation wherebynormally the system is balanced and no current is induced to flow insaid output windings in response to A. C.

current flow in said supply windings, a saturating winding on thecentral leg of each of said core members whereby in response to currentflow in one or the other of said saturating windings the system isunbalanced to provide an A. 'C. current at said output win-dings, an A.C. current source connected to said supply windings and to one phase ofsaid motor, means connecting said saturating windings to said electronicmembers, and means connecting said output windings to the second phaseof said motor.

3. The combination with at least two variable inductive devices adaptedfor developing sepa-.

rate signals of changing phase and amplitude and a two phase inductionmotor energized in accordance with the algebraic sum of said signals together with a controlled member driven by said motor, of amplifyingmeans connected to said devices and responsive to said signals as wellas to the phase thereof for determining the energization and thedirection of rotation of said motor, said means comprising a pair ofelectronic tubes, one or the other of which becomes conductive dependingupon the phase of said signals, saturable transformer means havinga pairof magnetically snoop permeable core members, each core member beingformed with a central leg and a pair or spaced parallel outer legs, A.0. supply windings on the outer legs oi both of said core membersconnected with each other in series aiding relation, A. C. outputwindings on the outer legs of both 01 said core members and connected inseries opposed relation whereby normally the system is balanced and nocurrent is induced to flow in said output windings in response to A. C.current now in said supply windings, a saturating winding on the centralleg of each of said core members whereby in response to current flow inone or the other of said saturating-windings the system is unbalanced toprovide an A. C. current at said output windings, an A. C. currentsource connected to said supply windings and to one phase of said motor,means connecting said saturating windings to said tubes, meansoonnectint said output windings to the second phase of said motor. and adrivable connection between said motor and one of said inductivedevices.

JOHN 1". N.

